As is known, magnetic field sensors are used in a variety of applications. One example application is in rotation detector circuits where a magnetic field sensor is used to detect rotation of an object, such as a ferromagnetic object, for example, a gear or ring magnet. In rotation detector circuits, the magnetic field associated with the object is typically detected by a magnetic field sensing element, such as a Hall effect element or a magnetoresistance element, which provides a signal (i.e., a magnetic field signal) proportional to a detected magnetic field.
Some rotation detectors generate an output signal indicative of the speed of rotation of the object. Other rotation detector circuits generate an output signal indicative of a direction of rotation of the object as well. One such rotation detector is described in U.S. Pat. No. 8,624,588 entitled “Apparatus and Method for Providing an Output Signal Indicative of a Speed of Rotation and a Direction of Rotation as a Ferromagnetic Object” which is assigned to the assignee of the present disclosure and incorporate herein by reference in its entirety.
Rotation detectors are widely used in automobile control systems, for example to detect rotation of an automobile wheel for use in anti-lock braking systems. During manufacture and/or use, magnetic field sensors sometimes present failures. Failures may be due to manufacturing defects, design defects, latent failures, damage caused by handling or during use, or some combination thereof.
In safety critical applications such as automobiles, various specified safety standards are required to be met in order to guarantee internal functionality of sensors. Compliance with such standards is intended to improve overall functional safety and result in higher quality and lower field failure rates.
To meet certain safety standards, some magnetic field sensor integrated circuits (ICs) contain built-in self-test circuitry and implement related self-test techniques. Self-test features are particularly important to detect failures occurring after installation of the device into its intended environment since, after installation, there are limited test opportunities due to reduced access to IC and interference of testing with normal operation of the device.